Packet-switched networks identify their nodes through a node address. The switching nodes transfer the data packets from a source to destinations identified by their respective node addresses. To that end, they use the routing information which can both be calculated centrally for the entire network, and calculated independently and distributed by each of the nodes in the packet-switched network. Distributed routing is used for example in IP networks. To converge into a stable network configuration, the nodes exchange their network view with their neighbors by means of the routing protocols. This view includes information about the topology (i.e., links between node) and the nodes served by a router (i.e., the address space or set of adjacent addresses working by means of a router).
The Internet network is an extremely complex network interconnecting known territories such as autonomous systems (AS). An AS is defined as a set of nodes configured with operation patterns common and consistent with relation to a set of networks. The routing protocols in the IP networks can be classified by their scope. Inner routing protocols, such as routing information protocol (RIP), open shortest path first protocol (OSPF) etc. are used within the scope of an AS. Outer routing protocols are used for exchanging information between the different AS. Currently, the only outer routing protocol known is the Border Gateway Protocol (BGP-4). To cause redundancy, many of the AS and the current Internet are connected to another two or more AS. This practice is known as multi-provider in the AS level.
Given the huge commercial success that the Internet has had, it has lead to the addresses from the IPv4 version being exhausted. To overcome this problem and to preserve the point-to-point principle established in Internet, a new version of the IP protocol, which is known as version IPv6, is being introduced and used in the network. This new version increases the available address space by means of increasing the length of the IP address field from 32 to 128 bits. The BGP-4 protocol is used in the IPv4 networks and it has been extended to deal with the IPv6 protocol version.
The addressing space of the current Internet IPv4 is not structured, which leads to a series of adverse effects such as the excessive growth of the number of routes in the Internet core routers. Therefore the IPv6 proposes a hierarchical delegation of the addressing space, in which the AS of IPv6 route the traffic following a simple rule: sending the traffic to the address space that was delegated to the bottom AS, lower hierarchical level, or to the top AS provider, higher hierarchical level, from which the address space was received. The IPv6 specifications do not provide the possibility of any other type of routing, which means that in the level of the AS, the Internet IPv6 consists of a series of routing trees connected to a complete mesh of high level domains. A large enough address space is assigned to the top AS providers, which is partially used by them and partially by their AS customers (located in a lower hierarchical level) to which the address space is delegated by means of aggregation, once they have their own customers. All the AS pass an input with their aggregated address space assigned to their top AS providers and inform their AS customers that they are the Internet default route. Thus the routing tables are kept small by aggregation, as is depicted in FIG. 1.
In order to prevent these drawbacks the Internet Engineering Task Force (IETF) has produced a detailed architecture for connecting the sites with IPv6 to more than one AS provider, and the AS multi-provider level has not been addressed.
This means that the level of the AS multi-provider for IPv6 as proposed by the IETF is only anticipated in the end customer level, whether the latter is a node (i.e., an ADSL router) or a site (i.e., a network of nodes with a single connection point), determining the following drawbacks:
1. Leaving all the technical responsibility of the multi-provider to the end user of the AS. In the case of a bigger organization, the task is carried out by the network operation centre or by the IT department at the expense of a bigger and highly qualified team.2. Using technologically advanced solutions which are not user friendly and are not feasible for retail services: a multi-provider service provider with end customers would have to handle a large amount of end customer devices with multiple addresses, and can no longer wait for the end customers to understand the implications of having multiple IP addresses assigned to their devices.3. Jeopardizing a significant part of the business of the wholesale IP service providers (such as TIWS (Telefónica complete international services), representing that any loss of an AS against a competing provider will virtually be lost forever, given that switching between providers means connectivity loss and longer transition periods.
The multi-provider in the AS level and the Internet IPv6 is technically possible, but it has still not been provided by the standards because it may be a source of serious problems, and would break the address delegation principle as has been described.
Furthermore, a potential source of uncontrolled growth of the routing tables of the core network of the Internet IPv6 would arise if the AS which depend on another AS were allowed to propagate their routing information to a bottom AS. The size of the routing table is a key factor both for the cost and for the performance of a router. With 128-bit address space instead of 32 bit, the size of the routing table could reduce the amount of physical memory which can be handled by the processors of the routers. The handling of the data structures of the size necessary to overcome this situation could be unfeasible due to the algorithm response time necessary for going through the routing tables.
Another solution to the problem described consists of implementing the BGP based on labeling and filtering which depend on the BGP communities which are optional BGP-4 attributes. The communities have a local meaning for a specific AS and are used for labeling announcements from the BGP-4. This labeling is then used through filters determining whether or not an announcement advances towards the routing process. This implementation proposal does not allow the AS multi-provider to have a single address space. The complete proposal requires the addressing to be delegated by the top AS.
Additionally, the AS multi-provider must label its prefixes with a label given in the form of a BGP community which must be accepted and correctly filtered by all the AS. This involves a consistent deployment strategy with uniform software editions in all the equipment of Internet IPv6. Currently there is a small set of well known communities which are uniformly accepted by all the sellers. Adding new well known values to this list is unlikely since the IETF will not back up the application in a near future.
Therefore, the implementation must take place as an agreement between providers and the risk of configuration errors cannot be disregarded.
Another solution which has been proposed consists of performing the virtual routing and forwarding (VRF) which is a methodology introduced by the router sellers to assign different, independent and isolated routing tables in a router. Isolation is the essential characteristics of the VRF.
The VRF is the corner stone for services such as virtual private networks (VPN). In a VPN environment, several customers could have the same address space and the essential characteristic is that the different customer networks co-exist in a router and that they are isolated from one another. The mixing of address spaces of different networks to provide a main source and another one to back-up the routing information is not foreseen. In fact, this characteristic goes against the basic concept of the VPN based on VRF and the routing information must be made available in a redundant manner, traditional routing mechanisms are used.